Pioneering Microbial Colonies in the Deep Biosphere

The deep subsurface biosphere is Earth’s largest biome, yet due to technical challenges and costs, sampling of this biome has remained limited resulting in limited knowledge of the life existing here. As seawater circulates through the permeable basaltic rocks in upper 500m of oceanic crust it oxidizes, hydrates, and cools the rock – releasing ions with oxidative potential into the fluids to support chemolithotrophy and lowering the temperature to be suitable for microbial life. The seawater carries with it microbes to colonize on the rock substrates, yet the community profile found in the rocks varies from the seawater. What has been sampled in this environment has come mostly from aged and altered rock, thus leaving a knowledge gap on the pioneering microbial communities on newly formed oceanic crust. The heterogenous composition of oceanic crust results in variation of available bioenergetics across the subseafloor biosphere. In this study we have investigated the microbial colonization of fresh basalt glass. Using 16S rRNA meta-barcoding, we investigated microbial communitiy composition. We explored the basalt hetergeneity as a factor in the pioneering microbial community composition as well as comparing the colonizing community to that of communities found in aged and altered basalts. This study provides insight to the diversity of life in the deep biosphere and the evolution of microbial communities within oceanic crust.